1. Field of the Invention
The present invention relates to a contact plate for use as a movable contact of a push-button switch, and more particularly to a disc contact plate press-formed into a dome shape, a sheet with the contact plate, and the structure of a switch device using the sheet.
2. Description of the Prior Art
Known structures of a contact plate for use as the movable contact of a push-button switch include the structures illustrated in FIG. 8 through FIG. 12. FIG. 8 through FIG. 10 are sectional views showing the relationship between a movable contact and a fixed contact, and FIGS. 11 and 12 illustrate the relationship between the manipulative force on and the shifted quantity of the movable contact.
FIG. 8 shows a state in which a disc movable contact 51 formed by cupping a thin metallic sheet into a dome shape is mounted over a central fixed contact 53 and a peripheral fixed contact 54, each similarly consisting of an electroconductive metallic sheet, arranged on the inner bottom face of a housing 52 consisting of synthetic resin or the like.
The movable contact 51 is formed of a skirt 51a rising from the outer circumference of a disc at a prescribed angle toward the center of the disc and a dome 51b, which is continuous from the skirt 51a and can be repetitively inverted. The skirt 51a and dome 51b are connected to each other by a smooth bend 51c. An outer peripheral end 51d of the skirt 51a is in contact with the peripheral fixed contact 54 at all times, and the inside of the top of the dome 51b constitutes a contact 51e, which comes into contact with the central fixed contact 53 when the dome 51b is repetitively inverted.
A gap is formed between the central fixed contact 53 and the peripheral fixed contact 54, with the central fixed contact 53 being formed a step below the peripheral fixed contact 54. As indicated by curve A in FIG. 11, when the dome 51b of the movable contact 51 is inverted the distance (shifted quantity) L1 between the contact 51e and the central fixed contact 53 can be greater by the level difference of the step, thus the shifted quantity after the inversion of the movable contact 51b can be set greater than otherwise, resulting in a crispy feeling of click. In the diagram the vertical axis represents the manipulative force F, and the horizontal axis represents the shifted quantity L.
Incidentally, AO in the diagram denotes the tactile sensation (click feeling) curve of the movable contact 51 and LA denotes the point where the reaction force after the inversion of the movable contact 51 is at its minimum, i.e., the settable maximum of the shifted quantity.
FIG. 9 illustrates a state in which the movable contact 51 is mounted over a circuit board 55 on which a circuit pattern is formed of a copper foil or the like. In this case, since a central fixed contact 56 and a peripheral fixed contact 57 are formed of a copper foil or the like in a planar form over the circuit board 55, the distance (the shifted quantity) L2 between the contact 5Se and the central fixed contact 56 is less than L1 when the dome 51b of the movable contact 51 is inverted.
FIG. 10 shows a movable contact 58 formed in a state in which the rising angle xcex8c of a skirt 58a is set more nearly upright than xcex8b shown in FIG. 9 (xcex8b less than xcex8c) so that when the dome 58b of the movable contact 58 is inverted the distance (the shifted quantity) L3 between a contact 58e and the central fixed contact 56 becomes equal to L1 (L3=L1). As indicated by curve C in FIG. 12, when the dome 58b of the movable contact 58 is inverted, the distance (the shifted quantity) L3 between the contact 58e and the central fixed contact 56 can be greater, the shifted quantity after the inversion of the movable contact 58 can be set greater than otherwise, resulting in a crispy feeling of click.
However, in the above-described structure of the movable contact 51 according to the prior art, when it is to be used in the planar circuit board 55 and when the dome 51b of the movable contact 51 is inverted, the distance (the shifted quantity) L2 between the contact 51e and the central fixed contact 56 is less than L1. The shifted quantity thus becomes smaller after the inversion of the movable contact 51 as indicated by B in FIG. 11, resulting in a problem of a dull feeling of click.
Further, if the rising angle xcex8c of the skirt 58a is increased, the reaction force of the tactile sensation curve CO of the movable contact 58 will take on a negative value at point LC as shown in FIG. 12, resulting in a problem that the movable contact 58 remains inverted instead of automatically returning to the original state.
An object of the present invention, therefore, is to solve the problems noted above and provide a movable contact structure which, even when used in a planar circuit board, can provide a crispy click feeling and will not fail to return to an original position after being inverted.
In order to solve the problems noted above, according to a first aspect of the invention, there is provided a contact plate consisting of a disc formed into a dome shape by cupping a center of a thin metallic sheet in one direction, provided with a skirt rising at a prescribed angle from an outer circumference of this disc toward a center of the disc, and a dome which is continuous from this skirt and can be repetitively inverted, the connecting part between the skirt and the dome being formed in multiple steps via a plurality of bent portions.
According to a second aspect of the invention, a projection in contact with a fixed contact is formed on an inner face of the dome.
According to a third aspect of the invention, an external face of the dome of the contact plate according to the first or second aspect of the invention is stuck to an adhesive back face layer of an insulating sheet, and the contact plate and an lower face of the insulating sheet are covered with a peelable protective sheet.
According to a fourth aspect of the invention, a spacer sheet having an accommodating hole for accommodating the contact plate is provided between the insulating sheet and the protective sheet.
According to a fifth aspect of the invention, the protective sheet of the sheet with the contact plate according to the third or fourth aspect of the invention is peeled, and the sheet with the contact plate after peeling is stuck to a circuit board, over which a plurality of fixed contacts are arranged, by the adhesive back face layer of the insulating sheet so that the contact plate is opposite the fixed contacts.
According to a sixth aspect of the invention, there is provided a switch device having the contact plate according to the first or second aspect of the invention and an accommodating section, whose inner bottom face is provided with a housing over which a fixed contact is arranged and a suppressing member liftably snapped into the accommodating section, wherein the contact plate is arranged opposite the fixed contact to be suppressible by the suppressing member.